1. Field of the Invention
The present invention relates to an exhaust gas purification apparatus for internal combustion engine provided with a catalytic converter and a secondary air introduction system.
2. Description of the Related Art
In general, a gas exhaust system of automobiles removes harmful components in an exhaust gas by a catalytic converter mounted to an exhaust gas pipe. That is, harmful components are purified in such a manner that when exhaust gas passes through the catalyst in the catalytic converter, the harmful components (CO, HC, NOx) in the exhaust gas are caused to make an oxidation reaction and reduction reaction by the catalyst.
A purification ratio achieved by these reactions changes depending upon an exhaust gas temperature and an air fuel ratio which is a ratio of fuel to air to be supplied into an internal combustion engine. Further, if a ternary catalyst containing noble metal such as platinum, vanadium or the like is used as the catalyst, the purification ratio achieved by the catalytic converter is maximized when the catalytic converter is at a temperature in an ordinary operation region (activation temperature: about 400.degree. C.) and the air fuel ratio is at a theoretical air fuel ratio.
However, when the internal combustion engine is not yet sufficiently warmed up (in a warming-up period) such as when it is just after being started, since the temperature of the catalyst is less than the above activation temperature and further the air fuel ratio is in a fuel rich range, a satisfactory purification ratio cannot be obtained to harmful components.
There are conventionally known an electric vehicle heating apparatus incorporating an electric heater for catalytic converter and an electrically-driven type secondary air introduction apparatus for supplying air to an exhaust gas pipe by an electrically-driven pump as technologies for solving the above problem.
As the conventional electric heating apparatus for a vehicle, there is a technology disclosed in Japanese Patent Publication No. 61-33735. FIG. 8 is a circuit diagram showing this apparatus. In FIG. 8, a generator, generally denoted at reference numeral 100, has a stator winding 101 connected to a controller 110 and a field winding 120 through a rectifier 102. A heating element 130, a battery 131 and an output adjusting means 121 are connected to the controller 110.
Further, the controller 110 is provided with first contacts 111,112, a second contact 113 and a control circuit 114.
The first contact 111 is interposed between the output terminal A of the rectifier 102 and the positive terminal of the battery 131. The first contact 112 is interposed between the rectifier 102 and the battery 131 with an end thereof connected to the output terminal I of the rectifier 102 and the other end connected to the positive terminal of the battery 131 through a charge alarm lamp 140 and a key switch 141. The other end of the first contact 112 is also connected to the field winding 120 through the output adjusting means 121.
The second contact 113 is interposed between the output terminal A of the rectifier 102 and the heating element 130.
Further, a control circuit 114 having a manual switch 115 is connected to the positive terminal of the battery 131.
Next, operation of the electric vehicle heating apparatus as constructed above will be described.
FIG. 8 shows that the positions of the respective contacts are in an ordinary charge control state and the heating element 130 is not heated.
In this state, an output from the stator winding 101 generated by supplying power to the field winding 120 is smoothed by the rectifier 102, supplied to the battery 131 from the output terminal A of the rectifier 102 through the first contact 111 and charges the battery 131.
Note, the power supplied to the field winding 120 is adjusted by the output adjusting means 121. More specifically, the output adjusting means 121 senses a voltage at the positive terminal of the battery 131 through the charge alarm lamp 140 and key switch 141 and when the terminal voltage is smaller than a predetermined set voltage (e.g. 14.5 V), an amount of a current to the field winding 120 is increased to increase an output of the stator winding 101. Thereafter, the voltage at the positive terminal of the battery 131 is increased by the increase of the output from the stator winding 101 and when the output reaches the above set voltage, the power supplied to the field winding 120 is stopped.
As described above, the voltage charged to the battery 131 is controlled constant by changing an amount of the current to the field winding 120 by comparing the voltage at the positive terminal of the battery 131 with the set voltage by the output adjusting means 121.
When the heating element 130 is placed in an operation start condition from the ordinary charge control state by turning on the manual switch 115 and second contact 113, the first contacts 111, 112 are turned off by the control circuit 114 of the controller 110.
With this arrangement, since the battery 131 is isolated from the output terminal A of the generator 100, the voltage at the positive terminal of the battery 131 is set to an open terminal voltage (about 12 V) and made lower than the set voltage (14.5 V). As a result, although the output adjusting means 121 increases the field current of the field winding 120, since a charging circuit is isolated by the first contact 111, the positive terminal voltage of the battery 131 does not increase and the field winding 120 is finally in a maximum excited state (fully excited).
Since only the electric load connected to the generator 100 is the heating element 130 here, the generator 100 entirely supplies a maximum output to the heating element 130 so that the heating element 130 is abruptly heated. While the heating element 130 is abruptly heated, power to be supplied to vehicle-mounted loads other than the heating element 130 is previously charged to the battery 131.
On the other hand, there is a technology disclosed in Japanese Patent Application Laid-Open No. 59-138714 as the conventional electrically-driven type secondary air introduction apparatus. FIG. 9 is a circuit diagram showing the apparatus.
In FIG. 9, an internal combustion engine has a cylinder 200 and an exhaust gas pipe 201 connected to a side wall of the cylinder 200. A catalytic converter 202 is inserted in the exhaust gas pipe 201 and a secondary air passage 210 is connected to the exhaust gas pipe 201 at a location upstream of the catalytic converter 202.
A secondary air pumping unit 220 comprising a pump 221 and a motor 222 is mounted to the secondary air passage 210. The motor 222 of the secondary air pumping unit 220 is connected to the battery 131 and a generator 100 through a secondary air relay 230 and controlled by a secondary air control circuit 240.
With this arrangement, the secondary air control circuit 240 supplies power to the exiting coil of the secondary air relay 230 and turns on the contact of the secondary air relay 230 after it confirms secondary air introducing conditions through information from various sensors. As a result, currents (e.g. 20 A) are supplied from the generator 100 and the battery 131 to the motor 222 through the contact of the secondary air relay 230 to rotate it. Air discharged from the pump 221 is supplied into the exhaust gas pipe 201 through the secondary air passage 210 by the rotation of the motor 222.
Incidentally, to cope with the recent strengthened regulation to an exhausted gas, harmful components must by further purified in a warming-up period. For this purpose, it is contemplated to use the electric vehicle heating apparatus and electrically-driven type secondary air introduction apparatuses shown in FIG. 8 and FIG. 9 in combination and operate them just after the start of a vehicle.
When these apparatuses are operated from just after the start of the vehicle, however, entire power needed by electric loads other than the heating element 130 is supplied from the battery 131 while the catalytic converter is abruptly heated by the heating element 130 in the electric heating apparatus. Thus, when secondary air is introduced by the electrically-driven type secondary air introduction apparatus during this period, the power from the battery 131 is greatly consumed by the motor 222 of the secondary air pumping unit 220 and the life of the battery 131 is greatly shortened. Further, since the voltage of the battery 131 lacks when the vehicle is started, the vehicle may cause engine stall. Further, since the power of the battery 131 is greatly consumed by the motor 222 of the secondary air pumping unit 220 before or after the abrupt heating of the catalyst, a problem also arises in that a voltage supplied to other general electric loads changes abruptly.
When the battery 131 having a large capacity is used to avoid these problems, there arise problems of the increased cost of manufacture and the increased overall size of the apparatus.